Upgrade to Java 21.

Author: khatchad

pom.xml

@@ -166,7 +166,7 @@
                 <version>3.6.2</version>
                 <configuration>
                     <aggregate>true</aggregate>
-                    <source>1.8</source>
+                    <source>21</source>
                     <encoding>UTF-8</encoding>
                     <maxmemory>1g</maxmemory>
                     <links>
@@ -418,7 +418,7 @@
                 <version>3.6.2</version>
                 <configuration>
                     <aggregate>true</aggregate>
-                    <source>1.8</source>
+                    <source>21</source>
                     <encoding>UTF-8</encoding>
                     <maxmemory>1g</maxmemory>
                     <debug>true</debug>